Flameproofing of construction material



United States Patent 3,383,274 FLAMEPROOFING 0F CQNSTRUCTION MATERIALDon W. Craig, Anderson, Califi, assignor to US. Plywood-Champion PapersInc., a corporation of New York Filed Jan. 6, 1965, Ser. No. 423,698

' Claims. (Cl. 161-162) The present invention is broadly concerned witha process for the manufacture of flameproof wood articles of superiorqualities and strengths, as well as with the manufactured articles perse. The invention is more particularly concerned with the improvedproduction of particle board, hardboard, bagasses, and other types offiber boards possessing excellent fire resisting and other high qualityphysical properties. The invention is especially concerned with a highquality board which comprises in combination a salt of ammonia, asynthetic resin, and a wood particle material; and with its method ofmanufacture. In accordance with a specific adaptation of the presentinvention, a superior fire resistant particle board is produced by thetechnique of adding crystals of ammonium salts at a critical time to thewood particles and resin, whereby these salts effectively distributethemselves throughout the mass of the board.

It is known in the art to utilize ammonium salts in order to modify andto attempt to render cellulose materials non-inflammable. However, onegreat commercial manufacturing problem is that it is very difficult tosecure a thorough and even distribution of the fire retardant chemicalwithin the board and particularly in sufficient quantity orconcentration to render the board substantially non-inflammable. Anotherproblem is that the treated material or board in many instances does notretain its mechanical strength and its desired surface quality andtexture when these salts are added. Techniques presentiy employed forthe commercial production of fire retardant or fire resistant particleboard is to first manufacture the board in one stage and thereafter in asubsequent stage treat the board with chemicals in order to render theboard non-inflammable or fire resistant. For example, one methodpresently used is to dissolve the fire retardant salt in an aqueoussolution and then soak the wood board in this solution in a bath whichis usually under pressure. Pressures which are generally employed are inthe range of from about atmospheric to 150 lb./sq. in. while thetemperatures of the soaking operation are in the range of about ambientF. to 190 F.

One ditficulty with this technique is that it is very difficult if notimpossible to posiiively and accurately control the amount of chemicalwhich is added to or impregnated in the wood. Another disadvantage isthat extensive relatively heavy equipment, such as the soakingequipment, for the effective and efficient handling, treating andconditioning of the boards is relaiively expensive. Furthermore, thissoaking technique requires prolonged periods of treating and dryingwhich lowers production, thus making the process expensive andundesirable. Also, when the treated board is dried, fire retardantchemicals are deposited on the surface of the board as the water orother solvent evaporates, which detracts from the surface quality. Ifsanding is required due to loss of surface quality, the fire retardantmaterial on the surface is removed, which decreases the fire resistivityof the board. On the other hand, if the efilorescence material is lefton the surface or if the concentration of the fire retardant material atthe surface of the wood is high, then difficulties are experienced infinishing the surface to the desired degree of luster. In many instancealso the dimensional stability is impaired as well as the resistance ofthe board to wetting.

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Another commercial technique presently utilized, particularly in themanufacture of fire retardant particle board, is to soak the woodparticles with the fire retardant material prior to the gluing stage orstep. In some instances when the wood particles used have'a highmoisture content in the range from 30 to by weight, and when the fireretardant chemical is highly water soluble the dry chemicals have beensprinkled on the wood chips, flakes, or particles prior to the gluingstep and the mixture allowed to stand until the diffusion of thechemicals into the particles is complete. Whenever this method of fireretardant treatment is done prior to gluing, the wet wood material mustbe dried before gluing, and as a result the fire retardant chemicals aredeposited on or near the wood surface as described hereinbefore. Also,at the high concentrations required for effective treatment, the surfacecoating of fire retardant chemical interferes substantially with theeffective bonding of the wood particles by the glue or resin. In someinstances, this may be compensated for by using higher concentrations ofthe hinder, or more expensive resins, or longer pressing times, or acombination of these factors, all of which substantially increasemanufacturing costs.

Thus, it has been discovered that when this wet technique is utilized,namely, the impregnation of the formed particle board or particles withthe fire retardant solution, loss of strength results, necessitatingincreased fabrication and finishing costs. In order to partially reducethe severe strength losses which result due to the soaking treatment, ahigher than normal concentration of the waterproof resin is used on thebinder. Also, surface roughing and variability of swelling which occursafter the treated panels are dried results in heavy material lossesduring the sanding operation. This also substantially increases the costof the operation.

The present invention produces a particle board of high quality and ofvery superior fire resistant qualities. The fireboard of the presentinvention also has excellent mechanical and surface properties which aresecured at a minimal cost. The particle board of the present inventionis characterized by having excellent physical properties as well ashaving excellent dimensional stability. Furthermore, excellent surfacefinishing and overlaying properties are secured.

The fire retardant product of the present invention in essence involvesa composition board comprising preferably three distinct layers havingan ammonium salt distributed in optimum concentrations through thelayers. This composition board of the present invention is secured by aunique improved process which may be readily understood by reference tothe drawing illustrating an embodiment of the same.

Reference is made to the drawing which is a diagrammatical sketch ordiagrammatical flow plan illustrating the manufacture of a three-layeror three-ply fire retard.- ant panel. Wood flakes or fiber particlesdesigned for the manufacture of a lower face ;layer are introduced intodrier and storage silo 4 by means of line or conveyor means 1. Woodflakes or fiber particles designed for the manufacture of a top facelayer are introduced into drier and storage silo 6 by means of line orconveyor means 3. The wood material for the manufacture of particleboards for the respective faces may be of various sizes andconfigurations, but preferably have dimensions of about 0.05 to 0.75"Width and 0.25 to 1.5" lengths and thicknesses of about 0.01 to 0.05inch.

A wide range of wood particle species and sizes can be utilized as facematerial. The choice is predominantly determined by what is availableand offers high strength properties, soft wood flakes that are cut fromplywood peeler cores are quite suitable. Another possibility is refinedfibers from hogged lumber and plywood residues or planer shavings. Thematerial selected depends upon the desired panel properties, e.g., longflakes and fibers provide high strength, small fragments produce asmooth surface. The effect of surface density on flame spread is notclear, however, bond strengths and density as related to ability of apanel to retain a layer of char is important. A smooth surface is alsobeneficial toward reduced flame spread, therefore weak fibers which tendto cause a hairy or fuzzy sanded surface should be avoided.

Driers 4 and 6 are maintained at temperatures in the range from aboutambient to 175 F. for a time period of about 3-5 minutes. (Face materialdrying is negligible for most raw materials.) The conditions are soadjusted that the moisture content of these chips are from about 17 to23 percent by weight moisure, preferably at about 20 weight percentmoisture. These particles therefore are relatively moist.

Resin or binder A is introduced and mixed with the wood chips removedfrom drier 4 by means of line 37 in blender 50, while resin or binder Cis introduced and mixed with the wood chips from drier 6 by means ofline 39 in blender 51. Resins A and C are mixed by any suitable meanswith the prepared, moist wood material such as with a rotating blenderand stationary spray nozzle or any suitable mixing means.

Wood material suitable for the manufacture of the core or center layeris introduced into drier by means of line 2. Generally, these particlesare of a different configuration than the face material. For example,the particle size core-plywood material may range from about 0.25 to 1.5inches in length to 0.05 to 1.0 inch in width to 0.01 to 0.2 inch inthickness.

Because contributions to flame spread and strength property are minimalin the core layer, material is determined by availability, economics andease of refining, and not so much by strength. This means that smallmaterial and weed species can be utilized. Flakes provide the tightestcore layer and therefore will have slower release of pyrolysis productsthan a particle core. Density effects are negligible outside ofconsolidation of a char layer. Resin B is mixed with the chips Withdrawnfrom drier 5 by means of line 38 in blender 52. Here again any suitablemeans of thoroughly mixing the chips with the resin may be employed.

The ammonium phosphate crystals are added as a dry powder to the mixtureof resin chips by means of lines 10, 11 and 12 at zones 7, 8 and 9,respectively. These salt crystals are preferably sprinkled onto the facewood particles and core wood particles by metering or control systems40, 41, 42 which accurately proportions the rate of crystal saltaddition to the calculated bone dry wood passing along conveyor belts orequivalent means 7, 8 and 9.

The salt addition occurs immediately after the wood material and binderemerges from the blenders where the resin is mixed with the wood chips.The addition of the dry crystals of salt should be within about minutes,preferably within 2 minutes.

The salt crystals are added as soon as possible after the resin additionand with as much agitation or tumbling as possible to effect maximumdistribution and adherence of the salt to the moist and tacky woodmaterial. If little mixing is achieved in the transfer of the gluedmaterial to the forming line spreader, then a separate mixing stageshould be introduced. The effectiveness of the salt and wood mixing iscritical, the length of time in mixing or after mixing until panelpressing is of little consequence. Since the glued material is tackiestjust out of the blender, this is the time to add the salt crystals.Thus, the immediate addition of the fire retardant salt crystals to thefreshly glued wood material is very important in obtaining the requireddispersion and adhesion of the crystals to the wood.

The mixtures of crystal, wood particles and resin then flow into hoppers13, 14 and 15 respectively onto weighing conveying belts or transferpoints 16, 17 and 18 respectively. The mixtures then flow throughhoppers 19, 20 and 21 onto conveying belts or caul plate which passes onat felting points 22, 23 and 24 respectively. The use of these mixinghoppers and transfer points and conveyor belts secures even distributionof the crystals throughout the mass of glued, moist wood particles.

The face material is at ambient temperature upon entering the blender.The only heating in the blender is produced by the resin which issprayed at 32 to 42 C. and therefore is negligible. The same resintemperatures are used in spraying the core material. This material maybe warm from the storage silo in the range from to F. but never over F.The wax sprayed 011 the core (approx. 1%) is heated to 265-285 F. andcontributes some heat but no attempt is made to heat the wood materialduring blending.

The salt crystals are not added to the blender because of plugging fromsalt gumming up the resin during spraying and because of ammonia fumes.

The respective chip mixtures are spread in layers on a caul plate atfelting points 22, 23, and 24 and then passed into a prepress 25, forbiscuit consolidation. (Press=l00- p.s.i.). The prepressed panel is theneasily loaded into the hot press 26. These presses are operated attemperatures in the range of about 320 F. to 375 F., preferably at atemperature of 350 F. for a time period of about 5 to 16 minutes, as forexample about 10 minutes. The pressures employed are in the range ofabout 225 to 400 lbs/sq. in., preferably at about 350 lbs/sq. in.

The panels are removed by means of line or conveyor 27. The finishedpanel is conveyed by means of line 27 and given a hot stack, at zone 28for about 20 to 30 minutes. The boards may be cooled in zone 29 and thenpassed to storage 30. Under certain conditions the boards may bypass thehot stack and passed directly to storage 30.

As pointed out, after the pressing cycle is completed, the hot panelsare immediately preferably given at least a 20 minute stacking whilehot. This hot stacking not only furthers the curet of the phenolicbinder, but increases the length of time the ammonium crystals areexposed to a hot and humid atmosphere. Thus, by the time the panels arecooled and have reached equilibrium moisture content conditions, thehighly effective distribution of the fire retardant chemicals throughoutthe wood particles will have been completed, thereby producing a veryexcellent flameproof wood structural member of high mechanical strength.

In the panels, under normal equilibrium moisture conditions, a largepercentage of the ion components that were in solution during pressingwill have reprecipitated as a thin effiorescence on the fiber surfacesand within the cellular structure of the fibers as the moisture leavesthe panel. Thus, excellent distribution and intimate contact of the fireretardant chemical with the wood is secured after the majority of theresin bonds between the wood particles have been made. Thus, this avoidsor overcomes almost entirely the interference and losses in strength ofthe panel which result when the wood is treated With the fire retardantmaterial before gluing.

The thicknesses of the face panels or plies as the core layer or ply maybe varied appreciably. Generally, the thicknesses of the face veneersare in the range of about to 7 inch, such as A; inch, while thethickness of the core ply is in the range of about A to 1 /2 inches suchas about inch.

As pointed out heretofore, the present invention comprises a combinationof the use of an ammonium salt in conjunction with a resin, preferably asynthetic resin and a wood material as, for example, wood chips. Thepreferred salts are the ammonium salts, preferably ammonium phosphatessuch as diammonium phosphate. Other less satisfactory salts are, forexample, monoammonium phosphate, ammonium bromide, ammonium sulphate,and the like.

With respect to the salt crystals, it is important that the size becontrolled if the final product is to have the salt effectivelydistributed throughout the mass and have excellent bond strength as wellas good surface qualities. For example, with a three-ply panelconstruction, it is preferred that the face veneers have very fine saltmaterials while the core layer will tolerate coarser salt crystals. Thepreferred results are obtained by grinding the salt crystals to lessthan 20 mesh (Taylor Standard screen scale) for the core ply and usingthe fines which pass through a 35 mesh screen for the face veneers orplies. The use of fines of salt in the critical face layers not onlygives excellent distribution and adherence of one ply to another, butalso solubilizes in the mass more completely during pressing. Thisleaves virtually no surface pitting following the sanding of the panel.

While various binders or resins may be used, it is preferred to use analkali catalyzed liquid phenol-formaldehyde resin in combination withdiammonium phosphate salts. However, the physical properties of thisresin must satisfy certain definite requirements. The further the resinis advanced or cross-linked, the shorter will be the time requirementduring pressing and the lower will be the loss in bonding efliciency asa result of resin migration into the wood. At the same time, the higherthe resin viscosity, the lower will be the spraying efliciency. Ofcourse, the resin may be heated during spraying to reduce viscosity, butthis approach is limited by the resin advancement that will occur duringstorage.

With regard to viscosity, the maximum viscosity that can be effectivelysprayed should be used. Usually this means a spraying viscosity of about150-200 c.p.s. at 25 C. Thus a. resin of over 200 to 400 c.p.s. at 25 C.can be heated up to 42 C. to reduce the spraying viscosity to thedesired level without drastically shortening the pot life of the resinin the stand tanks. Therefore, viscosity used will depend on thecapabilities of the spraying equipment.

The resin solids or resin concentration used depends on the moisturecontent of the wood material at the blenders and the final moisturecontent desired before pressing and the amount of resin to be added. Forwood moisture contents of and 3% and resin additions of 12 and 6.5%(based on ODW) for face and core material respectively, the finalmoisture content of approximately 33.5 and 8.5% will be achieved byusing a resin solids concentration of 40%. The range for a desiredoperation would be 37 to 43%. Where resin is added during fiberrefining, the resin solids may go as low as 12%.

This method is limited by the amount of resin sprayed on the wood andthe moisture tolerance of the particle board during pressing. Forprocess variables and equipment used in this invention, the resinadvancement must be kept between 150 and 400 centipoises and preferablyabout 175 centipoises at C. and at a spraying temperature of about 32 to42 C. Thus, the viscosity of the resin when sent through the sprayingequipment should be 150 to 200 c.p.s. to obtain effective resindistribution and rate of application. This will change somewhataccording to the equipment used and the amount of resin to add within agiven period of time.

The concentration of the resin used in one operation was at 43% resinsolids based on the total weight of the solution. The sodium hydroxideconcentration of the resin was also carefully controlled within 4.5 to5.4%. Since the ammonium salts have a buffering action or slowing of thecure rate of the resin, more caustic must be added than is ordinarilyused in the phenolic bonded particle board as for example about 0.5 to2.5%.

The alkali is usually added as 50% sodium hydroxide. The concentrationand amount added is taken into account when calculating the resin solidsand amount of water added. For this process, the desired alkali contentis present when the resin is purchased in the concentrate form (approx.50% R.S.); only water is added during advancement cooking. However,above a certain caustic level, i.e., above about 5% of resin solidsadded, in the finished panel the swelling and water absorptionproperties and the stability of the resin bonds are noticeably degraded.The sodium hydroxide concentration used in combination with Douglas Fir,Western Pine, and White Fir wood material is about 4.7%. The use of lessacidic wood species permits a decrease in the caustic concentration.

With woods of nearly neutral or slightly acidic pH, the sodium hydroxideconcentration will still have to be maintained at a comparatively highlevel due to the buffering of the ammonium salt. A sodium hydroxideconcentration above about 4% but not more than about 5% would encompassall changes due to species acidity (percent based on resin solids).

The three layer or three veneer construction particle board of thisinvention affords a high :degree of flexibility in producing a superiorand strong fire retardant commercial product. This is secured bycontrolling the material which makes up each individual layer. It ispossible and very desirable to add higher concentrations of the fireretardant chemical or salt in the face layer than in the core layer, oronly in the face layer. The diammonium phosphate or an equivalent saltor crystal may be used in both of the face layers and also in the corelayer.

The amount of fire retardant salt used may be varied appreciably *but itis preferably in the range from about 15 to 30 wt. percent, preferablyin the range of about 20 to 25 wt. percent as, for example, about 22 wt.percent based on the oven dry weight of the wood particles in the panel.At a 15% by wt. percent diammonium phosphate concentration in the corelayer, (range 10 to 20% by wt.), and 22% diammonium phospate in the facelayer plus the use of high quality cut Douglas Fir for the face flakes(range 20% to 30% by wt.), a high density face layer is produced whichis very effective in resisting flame spread and retarding the escape ofinflammable pyrolysis products from within the panel.

A particular adaptation of the present invention is to have a variedmoisture content in the face layer or face ply which differs from themoisture content of the core ply. It is preferred that the moisturecontent in a glued face ply prior to pressing be in the range from about25 to 40 wt. percent as, for example, about 33 wt. percent and the resinsolids at about 11% or in the range of 8 to 15% based on the oven dryweight of the wood. The face material moisture content will be greaterthan bone :dry and probably 8 to 25%, and preferably 20%. When the resinis added, the water present brings up the moisture content according tothe resin solids used. In this way the moisture content is controlled.The low cost White Fir and Western Pine coarse particles for the coreare approximately 7 to 11 wt. percent moisture content after gluing as,for example, about 9 wt. percent moisture content and about 5 to 9 wt.percent solids as, for example, about 7% resin solids.

The core material is usually dried to 3% before gluing. After the resinis applied the moisture content is raised according to the resin solids.The term bone dry wood (BDW) is used to designate the base upon whichthe amount of resin added or wood used is calculated. This is becausethe moisture content of the wood is constantly changing duringprocessing.

The use of a higher moisture content in the outer layers with respect toa fi-ameproof member provides a very important advantage over singlelayer boards or plies where the moisture is uniformly distributedthroughout the panel. When the moisture content is only in the facepanel, the steam generated will pass through the face flakes and intoand out through the core layer, causing dissolution and disass-ocia-tionof the ammonium salts. The ions formed after solvati-on of the crystalsthen diffuse into the fiber structure. This etfect is greatest in theface material where the flame spread is the most critical. The moisturein the face layer also plasticizes the wood to form a very smooth, highdensity face layer with excellent physical properties.

There are no further requirements after pressing insofar as fireretardant treatment is concerned. Very little degradation or materialloss is incurred from efilorescence on the surface of the panel becausemost of the moisture in the panel is driven into the center and out ofthe edges of the core during pressing. No further time is required inthe board forming process as the fire retardant materials are added andthe glue materials are transferred to the storage bin. The total cost offire retardant treatment is far below the cost of other processes.

Thus, the present invention is concerned with the use of particular typecrystals which are applied to a mixture of wood flakes and glue at apredetermined time after the glue and wood flakes are mixed. By thistechnique, the diffusion of the crystals such as the diammoniumphosphate crystals throughout the entire mass of the wood and resin issecured while, at the same time, the mechanical strength and otherdesirable characteristics of the panel remain unimpaired. Furthermore,by the use of particular size crystals in the face veneers and the useof relatively coarse crystals in the core, additional mechanicalfeatures are secured. In addition, by the control of the moisturecontent prior to pressing in the face veneers as compared to the totalmoisture content in the core, additional unexpected desirable featuresare secured.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A fiameproof wood article of superior quality and strength whichcomprises a lower face layer of adhered small dimensioned wood particleshaving uniformly distributed therethrough crystals of an ammonium salttaken from the group consisting of ammonium phosphates, ammonium bromideand ammonium sulphate, a core layer of adhered large dimensioned woodparticles having uniformly distributed therethrough crystals of saidammonium salt, a top face layer of adhered small dimensioned woodparticles having uniformly distributed therethrough crystals of saidammonium salt, said layers being rigidly adhered to one another by aresin binder.

2. Article as defined by claim 1 wherein the particles in said lowerface layer and said top face layer have dimensions of about .05 to .75"in width, about .25 to 1.5" in length and about .01 to .05 thick; andwherein the particles in said core layer have dimensions of about .05 to1.0" in width, about .25 to 1.5" in length and about .01 to .2" thickand wherein said salt is an ammonium phosphate salt and the coreparticles are always of greater dimensions than the face layerparticles.

3. Article as defined by claim 1 wherein said salt is diammoniumphosphate.

4. Article as defined by claim 3 wherein the size of the salt crystalsin the face layers are less than about 20 mesh, and the size of the saltcrystals in the core layer are about 2035 mesh.

5. Article as defined by claim 4 wherein the moisture content in theface layers is in the range of about 20 to 40 wt. percent and whereinthe moisture content in the core layer is in the range of about 7-11 wt.percent.

6. Article as defined by claim 1 wherein said particles are adhered bymeans of an alkali catalyzed liquid-phenolformaldehyde resin, andwherein said ammonium salt is an ammonium phosphate salt.

7. Article as defined by claim 1 wherein said face layers are about tothick, wherein said core is about A to 1%" thick, and wherein saidarticle contains from about 15 to 30 wt. percent of an ammoniumphosphate salt distributed therethrough.

8. Article as defined by claim 1 wherein said face layers contain fromabout 20 to 30 wt. percent of an ammonium salt distributed therethrough,and wherein said core layer contains from about 10 to 20 wt. percent ofan ammonium salt distributed therethrough.

9. Article as defined by claim 8 wherein said face layers contain about22 wt. percent of an ammonium phosphate and wherein said core containsabout 15% by weight of an ammonium phosphate.

10. Process for the production of a strong, high quality flameproofparticle board which comprises, (1) mixing relatively small dimensionedwood particles with a binding resin, (2) mixing relatively largedimensioned wood particles with a binding resin, (3) directly thereafteradding dry crystals of an ammonium salt taken from the group consistingof ammonium phosphates, ammonium bromide and ammonium sulphate to themixture of relatively small dimensioned wood particles and resin, and tothe mixture of relatively large dimensioned wood particles and resin,said ammonium salt being present in a higher concentration in said smalldimensioned wood particles and a lower concentration in said largedimensioned wood particles, (4) thereafter positioning a core layer ofrelatively large dimensioned wood particles and resin intermediate a topface layer and a bottom face layer of said relatively small dimensionedparticles and resin, (5) thereafter pressing the same, whereby a threelayer particle board is secured having the ammonium salt crystalsdistributed therethrough.

11. Process as defined by claim 10 wherein said resin is an alkalicatalyzed liquid-phenol-formaldehyde resin, and wherein said salt is anammonium phosphate salt.

12. Process as defined by claim 10 wherein said salt is an ammoniumphosphate salt, wherein the concentration of the salt in said facelayers is in the range of between 20 to 30% by weight and wherein theconcentration of the salt in said core layer is in the range from about10 to less than 20% by weight.

13. Process as defined by claim 10 wherein said particles are dried to amoisture content between about 17 to 23% by weight before mixing withsaid resin and wherein said layers are pressed at a temperature in therange of about 320 F. to 375 F. and at a pressure in the range fromabout 225 to 400 lbs/sq. in.

14. Process as defined by claim 13 wherein the drying step and theconcentration of the resin are controlled to have a moisture content insaid face layers in the range from about 20 to 40% by weight, andwherein the moisture content in the core is in the range from about 7 to11% by weight in the finished product.

15. Process as defined by claim 10 wherein the viscosity of said resinwhen mixed with said particles is in the range from about to 200 cps.

References Cited UNITED STATES PATENTS 2,859,187 ll/l958 Ropella 161-1682,891,019 6/1959 Ericks 260l72 3,050,424 8/1962 Schmitt 16l--403 ROBERTF. BURNETT, Primary Examiner.

W. J. VANBALEN, Assistant Examiner.

1. A FLAMEPROOF WOOD ARTICLE OF SUPERIOR QUALITY AND STRENGTH WHICHCOMPRISES A LOWER FACE LAYER OF ADHERED SMALL DIMENSIONED WOOD PARTICLESHAVING UNIFORMLY DISTRIBUTED THERETHROUGH CRYSTALS OF AN AMMONIUM SALTTAKEN FROM THE GROUP CONSISTING OF AMMONIUM PHOSPHATES, AMMONIUM BROMIDEAND AMMONIUM SULPHATE, A CORE LAYER OF ADHERED LARGE DIMENSIONED WOODPARTICLES HAVING UNIFORMLY DISTRIBUTED THERETHROUGH CRYSTALS OF SAIDAMMONIUM SALT, A TOP FACE LAYER OF ADHERED SMALL DIMENSIONED WOODPARTICLES HAVING UNIFORMLY DISTRIBUTED THERETHROUGH CRYSTALS OF SAIDAMMONIUM SALT, SAID LAYERS BEING RIGIDLY ADHERED TO ONE ANOTHER BY ARESIN BINDER.